From waste to wealth: iron oxide doped hydroxyapatite-based biosensor for the colorimetric detection of ascorbic acid

Ascorbic acid plays a pivotal role in the human body. It maintains the robustness, enlargement, and elasticity of the collagen triple helix. However, the abnormal concentration of ascorbic acid causes various diseases, such as scurvy, cardiovascular diseases, gingival bleeding, urinary stones, diarrhea, stomach convulsions, etc. In the present work, an iron-doped hydroxyapatite (HAp@Fe₂O₃)-based biosensor was developed for the colorimetric detection of ascorbic acid based on a low-cost, biocompatible, and ubiquitous material. Due to the catalytic nature of HAp owing to the acidic and basic moieties within the structure, it was used as a template for HAp@Fe₂O₃ synthesis. This approach provides an active as well as large surface area for the sensing of ascorbic acid. The synthesized platform was characterized by various techniques, such as UV-Vis, FTIR, SEM, XRD, TGA, EDX, etc. The HAp@Fe₂O₃ demonstrated inherent peroxidase-like activity in the presence of 3,3',5,5'-tetramethylbenzidine (TMB) oxidized with the assistance of H₂O₂. It resulted in the color changing to blue-green, and after the addition of ascorbic acid, the color changed to colorless, resulting in the reduction of TMB. To achieve optimal sensing parameters, experimental conditions were optimized. The quantity of HAp@Fe₂O₃, H₂O₂, pH, TMB, time, and the concentration of ascorbic acid were fine-tuned. The linear range for the proposed sensor was 0.6-56 μM, along with a limit of detection of 0.16 μM and a limit of quantification of 0.53 μM. The proposed sensor detects ascorbic acid within 75 seconds at room temperature. The proposed platform was also applied to quantitatively check the concentration of ascorbic acid in a physiological solution.